START AND OPERATION SEQUENCES FOR HYBRID MOTOR VEHICLES
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to hybrid motor vehicles and, more
particularly, to a hybrid powertrain system adapted for installation in a hybrid motor vehicle.
[0002] Automobile manufacturers are constantly working to improve fuel efficiency in
motor vehicles. Improvements in fuel efficiency are typically directed toward reducing weight,
improving aerodynamics, and reducing power losses through the vehicle powertrain. However,
the need to improve fuel efficiency is commonly offset by the need to provide enhanced comfort
and convenience to the vehicle operator. As an example, manually-shifted transmissions are
more fuel efficient than automatic transmissions due to lower parasitic losses. The higher losses
associated with conventional automatic transmissions originate in the torque converter, the plate
clutches and the hydraulic pump used to control operation of the hydraulic shift system.
However, a vast majority of domestic motor vehicles, for example, are equipped with automatic
transmissions due to the increased operator convenience they provide. Recent advances in
power-operated shift systems have allowed development of "automated" versions of manual
transmissions, which automatically shift between sequential gear ratios without any input from
the vehicle operator. Thus, automated manual transmissions provide the convenience of a
traditional automatic transmission with the efficiency of a manual transmission.
[0003] Passenger vehicle and heavy truck manufacturers are also actively working to
develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted
into the air by conventional powertrain systems equipped with internal combustion engines.
Significant development efforts have been directed to electric and fuel-cell vehicles.
Unfortunately, these alternative powertrain systems suffer from several disadvantages and, for
all practical purposes, are still under development. However, "hybrid" electric vehicles, which
include an internal combustion engine and an electric or hydraulic motor, offer a compromise
between traditional internal combustion engine powered vehicles and full electric powered
vehicles. These hybrid vehicles are equipped with an internal combustion engine and an electric
motor that can be operated independently or in combination to provide motive power to the
vehicle.

[0004] There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid
vehicles. In a series hybrid vehicle, power is delivered to the wheels by the electric motor,
which draws electrical energy from a generator or battery. The engine is used in series hybrid
vehicles to drive a generator that supplies power directly to the electric motor or charges the
battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles,
the electric motor and the engine can be operated independently or in combination pursuant to
the running conditions of the vehicle.
[0005] Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load
mode where only the electric motor is used to drive the vehicle, a high-load mode where only the
engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric
motor are both used to drive the vehicle. However, prior art parallel hybrid powertrain systems
are relatively inefficient at transitioning from one mode to another, particularly the transition
from low-load mode to high-load mode. Furthermore, a majority of prior art hybrid powertrain
systems are designed for use in passenger vehicles that employ a relatively light duty gasoline or
diesel engine, as opposed to the relatively heavy duty diesel engines found in over-the-road
trucks. While hybrid powertrain systems employing a light duty gasoline or diesel engine may
be readily transitioned from one operating mode to another without any perceived transition
event by the vehicle operator, prior art powertrain systems employing a heavy duty diesel engine
are notoriously unsmooth during the transition from one operating mode to another, particularly
when the diesel engine is started. Accordingly, there exists a need for improved hybrid
powertrain systems that facilitate an efficient and smooth transition from one operating mode to
another, particularly in vehicles that employ a heavy duty diesel engine.
BRIEF SUMMARY OF THE INVENTION
[0006] A vehicular hybrid powertrain system is provided that includes a first prime mover
having an output shaft, a multi-ratio transmission having an input, and a second prime mover
having an output connected to the first prime mover output through a first power path and to the
transmission input through a second power path. The first power path is configured to receive
power from the second prime mover during a first operating mode to drive rotation of the
transmission input and the second power path is configured to receive power from the second
prime mover during a second operating mode to drive rotation of the first prime mover output.

The second prime mover output is configured to rotate in a first direction in the first operating
mode to transmit power to the first power path and in a second direction in the second operating
mode to transmit power to the second power path. A method of operating a vehicular hybrid
powertrain system is also provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[0008] FIG. 1 is a schematic view of a hybrid powertrain system for a motor vehicle;
[0009] FIG. 2 is a schematic view of a multi-ratio hybrid transmission according to an
embodiment of the present invention and adapted for use in the hybrid powertrain system shown
in FIG. 1;
[0010] FIG. 3 is a schematic view of a multi-ratio hybrid transmission of FIG. 2, shown
during a second mode of operation;
[0011] FIG. 4 is a schematic view of a multi-ratio hybrid transmission of FIG. 2, shown
during a third mode of operation;
[0012] FIG. 5 is a schematic view of a multi-ratio hybrid transmission according to another
embodiment of the present invention and adapted for use in the hybrid powertrain system shown
in FIG. l;and
[0013] FIG. 6 is a detailed view of the multi-ratio hybrid transmission of FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Referring to FIG. 1, a hybrid powertrain system 20 is shown in accordance with an
embodiment of the present invention. In the illustrated embodiment, powertrain system 20
includes a first prime mover 22, such as a spark-ignited or compression-ignited internal
combustion engine, and a hybrid transmission 24 that includes a second prime mover 26 (see
FIG. 2), such as an electric motor/generator or hydraulic motor/pump. A main clutch 28 is

positioned between first prime mover 22 and hybrid transmission 24 to selectively
engage/disengage first prime mover 22 from hybrid transmission 24.
[0015] To facilitate operation of first prime mover 22 and hybrid transmission 24,
powertrain system 20 may include an electronic control unit (ECU) 30 for controlling operation
of first prime mover 22, main clutch 28, and hybrid transmission 24. In a particular
configuration, ECU 30 includes a programmable digital computer that is configured to receive
various input signals, including without limitation, the operating speeds of first and second
prime movers 22 and 26, transmission input speed, selected transmission ratio, transmission
output speed and vehicle speed, and processes these signals accordingly to logic rules to control
operation of powertrain system 20. For example, ECU 30 may be programmed to deliver fuel to
first prime mover 22 when first prime mover 22 functions as an internal combustion engine. To
support this control, each of first prime mover 22, main clutch 28 and hybrid transmission 24
may include its own controller 32, 34 and 36, respectively. However, it will be appreciated that
the present invention is not limited to any particular type or configuration of ECU 30, controllers
32, 34 and 36, or to any specific control logic for governing operation of hybrid powertrain
system 20.
[0016] In the illustrated embodiment, powertrain system 20 also includes at least one energy
storage device 38 for providing energy to operate first and second prime movers 22, 26. For
example, energy storage device 38A may contain a hydrocarbon fuel when first prime mover 22
functions as an internal combustion engine. In another example, energy storage device 38B may
include a battery, a bank of batteries or a capacitor when second prime mover 26 functions as an
electric motor/generator. When so configured, the electric motor-generator may be provided in
electrical communication with electrical storage device 38B through a drive inverter 39, as is
known in the art. Alternatively, energy storage device 38B may function as a hydraulic
accumulator when second prime mover 26 functions as a hydraulic motor/pump.
[0017] With reference to FIGS. 2-4 of the accompanying drawings, the components and
function of hybrid transmission 24 will now be described in greater detail. In an embodiment,
hybrid transmission 24 is connected to the output of first prime mover 22 by main clutch 28,
which includes a first main clutch shaft 40 and a second main clutch shaft 41 (which also
functions as the first prime mover output shaft when no main clutch is used). For illustration,

prime mover 22 is shown as an internal combustion engine in FIGS. 2-4, which generally
includes a flywheel 42 for reference. In addition to second prime mover 26, hybrid transmission
24 also includes an input shaft 44, an output shaft 46, a planetary gearset 48, a control
mechanism 50 and a multi-ratio transmission 52. Multi-ratio transmission 52 may include a
number of interchangeable gear ratios, as found in any number of change-gear transmissions
known in the art, or may include a less traditional power transmission system, such as a
continuously variable transmission ("CVT").
[0018] In an embodiment, hybrid transmission 24 also includes first and second power paths
54, 56 for transmitting power between second prime mover 26 and second main clutch shaft 41
and/or transmission input shaft 44. As shown in FIG. 2, first power path 54 may include a first
gear train having an input shaft gear 58 secured for rotation with input shaft 44, a first pinion
gear 60 and a first headset gear 62. Similarly, second power path 56 may include a second gear
train having a main clutch shaft gear 64 secured for rotation with main clutch shaft 41, a second
pinion gear 66 and a second headset gear 68. In an embodiment, first power path 54 is
approximately 98% the ratio of second power path 56 to prevent undesirable gear lock-up during
operation of hybrid transmission 24. Alternatively, first and second power paths 54, 56 may
include a chain or belt between input shaft gears 58, 64 and headset gears 62, 68, in which case
pinion gears 60, 66 would not be needed.
[0019] Second prime mover 26 is connected to a countershaft 70, upon which first and
second headset gears 62, 68 are rotatably supported. Countershaft 70 and second prime mover
26 are selectively connected for rotation with second headset gear 68 by a single acting
synchronizer clutch 72, which is axially movable to connect a collar 74 rotatably supported on
countershaft 70 to countershaft 70 itself. To support collar 74, second headset gear 68 may
include a generally cylindrical receptacle 76 within which collar 74 is received. Because collar
74 and countershaft 70 are rotatably supported by second headset gear 68, a first overrunning
clutch 78 is positioned between receptacle 76 and collar 74 to selectively secure collar 74 for
rotation with second headset gear 68. The term "overrunning clutch" includes, without
limitation, various automated and power-operated, single or dual-mode clutches; wherein
operation in an "engaged" mode results in a single or bi-directional clutching action and
operation in a "disengaged" mode permits freewheeling in one or both rotational directions.

Thus, when clutch 76 is in an "engaged" mode, collar 74 is secured for rotation with second
headset gear 68 in at least one rotational direction.
[0020] Second prime mover 26 is selectively connectable to first power path 54 through
planetary gearset 48. When so configured, countershaft 70 includes a sun gear 82 secured for
rotation therewith and first headset gear 62 includes a ring gear portion 84 fixed to rotate with
first headset gear 62. Between sun gear 82 and ring gear portion 84 are a number of planet gears .
86 meshed with sun gear 82 and ring gear portion 84. Planet gears 86 are rotatably supported by
a planet carrier 88, which in turn is rotatably supported by a second overrunning clutch 90 that is
secured to a transmission housing or other fixed structural component. Second prime mover 26
is also selectively connectable to first power path 54 through a jaw clutch 91, which is axially
movable on countershaft 70 to secure countershaft 70 for rotation with first headset gear 62.
[0021] To facilitate the connection of second prime mover 26 to first or second power path
54, 56 via jaw clutch 91 or synchronizer clutch 72, respectively, hybrid transmission 24 may
also include clutch control mechanism 50 for controlling movement of clutches 72 and 91. In
the illustrated embodiment, which is not intended to limit the scope of the invention, clutch
control mechanism 50 is a kinematic mechanism that includes a pair of spring biased lever arms
92, 94 and linkage 96 that couples lever arms 92, 94 for movement with a screw member 98 that
forms a portion of a motor-driven screw actuator 100. In a particular configuration, linkage 96
includes a first linkage member 102 that extends through a support member 104, which may be
secured to the transmission housing or other fixed structure, and lever arm 94 and terminates in
an end cap 108. A resiliency compressible member 106, such as a compression spring, is
positioned between lever arm 94 and support member 104 to apply a biasing force against lever
arm 94 toward end cap 108. Similarly, a second linkage member 110 is moveably linked to first
linkage member 102 via a pivotable link 111, which is secured to the transmission housing or
other fixed structure proximate its midsection. A second resiliency compressible member 112
biases lever arm 94 against a stop 114. As shown in FIG. 4, the motor driven screw actuator 100
may be rotated to draw screw member 98 and first linage member 102 closer to actuator 100,
thereby effecting axial movement in lever arms 92, 94 and their corresponding clutch.
[0022] As shown in FIG. 2, planetary gearset 48 is arranged so that when second prime
mover 26 is operating to rotate countershaft 70 in a first angular direction (such as the

counterclockwise direction illustrated in FIG. 2) and overrunning clutch 90 is "engaged", planet
carrier 88 is prohibited from rotating causing the rotational power from countershaft 70 to be
transmitted through planetary gears 86 and into ring gear portion 84 at a predetermined gear
ratio (typically a gear reduction). Rotational power is transmitted into first power path 54
through first headset gear 62 and then into multi-ratio transmission 52 through transmission
input shaft 44. In this mode of operation, second prime mover 26 may be operated to smoothly
launch a vehicle employing hybrid transmission 24 without the assistance of first prime mover
22.
[0023] When a predetermined vehicle speed is achieved, the system may be operated to
transmit power from second prime mover 26 to first prime mover 22 by reversing the rotation of
countershaft 70 (see, e.g., FIG. 3). This feature allows overrunning clutch 90 to be disengaged,
planetary gearset 48 to freewheel, and overrunning clutch 78 to be engaged, all of which occur at
roughly 0 RPM of the countershaft. Rotational power may then be transferred from second
prime mover 26 through countershaft 70 and into second power path 56 via second headset gear
68. More particularly, rotational power is transmitted from countershaft 70 into collar 74
through synchronizer clutch 72 and from collar 74 into second headset gear 68 through the
engaged overrunning clutch 78. The rotational power produced by second prime mover 26 is
then transmitted from second power path 56 into second main clutch shaft 41. Provided main
clutch 28 is engaged, power may be transferred through main clutch 28 into first prime mover 22
through first main clutch shaft 40. A third overrunning clutch 116 may be positioned between
second main clutch shaft 41 and transmission input shaft 44 to allow for different rotational
speeds between the two shafts. In this mode of operation, rotational power from second prime
mover 26 may be used to start first prime mover 22 functioning as an internal combustion
engine.
[0024] When second prime mover functions as an electric motor/generator or a hydraulic
motor/pump, rotation of countershaft 70 may be quickly reversed to facilitate the transfer of
power from first power path 54 to second power path 56. Thus, when the motor speed decreases
to zero (during the transition from one rotating direction to another) and then begins to increase
in the other direction, overrunning clutch 78 engages and begins cranking the engine and driving
it toward the speed of transmission input shaft 44 that is being maintained by vehicle inertia.

When first prime mover 22 starts, the speed of first prime mover 22 is quickly increased under
the assistance of second prime mover 26, which provides for a relatively smooth start and engine
acceleration sequence. This feature is particularly useful in powertrain systems that employ
heavy duty diesel engines that start roughly and slowly increase in speed when not assisted, to
smoothly transition the powertrain system to "parallel" operation. Overrunning clutch 116 may
then be engaged when the speed of second main clutch shaft 41 and transmission input shaft 44
are substantially equal. During the time second main clutch shaft 41 is accelerating, there is
generally no power being applied to transmission input shaft 44, allowing a gear ratio change to
occur between a first gear ratio and a second gear ratio (or between any other gear ratios). In a
vehicle employing an internal combustion engine as the first prime mover and an
electric/hydraulic motor as the second prime mover 26, the above event results in a smooth and
efficient switch from all electric/hydraulic drive, to engine-electric/hydraulic parallel drive, all
while starting the engine and conducting a gear ratio change in the transmission virtually
simultaneously.
[0025] Overrunning clutch 116 may be configured as a one-way clutch, which allows
"positive" driveline torque to flow through clutch 116 in a direction from first prime mover 22
toward multi-ratio transmission 52 and prevents torque-flow in the opposite direction (so called
"negative" driveline torque). This feature allows first prime mover 22 to be reduced to an idle
speed or even shut down anytime it is not providing positive driveline torque. Overrunning
clutch 116 also isolates first prime mover 22 during the start sequence to ensure no driveline
reaction torque is imposed thereon (e.g., no negative torque, compression pulses, etc.).
[0026] In conventional non-hybrid powertrain systems, negative driveline torque is absorbed
by the vehicle engine and/or brakes and is therefore lost energy. However, in hybrid
transmission 24, this torque may be used to drive rotation of second prime mover 26 operating as
a generator or pump to create and store energy in energy storage device 38B. Moreover, engine
braking may be emulated, which may be desirable, if energy storage device 38B is at capacity.
Clutch 216 may remain engaged and normal engine braking will occur. Particularly,
synchronizer clutch 72 may be disengaged and jaw clutch 91 may be engaged to directly connect
countershaft 70 with first headset gear 62. In this mode of operation, negative driveline torque

may be transmitted from transmission input shaft 44 through first power path 54 and into second
prime mover 26 via countershaft 70.
[0027] Additionally, when less than full power is being requested from first prime mover 22,
a portion of the power generated by first prime mover 22 and applied to multi-gear transmission
52 through input shaft 44 may be routed through first power path 54 and into second prime
mover 26 via either planetary gearset 48 or jaw clutch 91. In this mode of operation, the routed
power from first prime mover 22 may be used to drive second prime mover 26 functioning as a
generator or pump to store energy in energy storage device 38B. This mode of operation may
occur at any time during operation of first prime mover 22, even when the vehicle is at rest and
the transmission 52 is in neutral. Furthermore, when second prime mover 26 functions as an
electric generator, first prime mover 22 may be used to selectively drive second prime mover 26
to supply electric power for on-board or off-board electrical equipment via the existing drive
inverter. Similarly, when second prime mover 26 functions as a hydraulic pump, first prime
mover 22 may be used to selectively drive second prime mover 26 to provide fluid power for on-
board or off-board hydraulic equipment.
[0028] While the features of the present invention are particularly suited for transitioning
between operating sequences while the vehicle is moving, it is possible to operate second prime
mover 26 to start first prime mover 22 functioning as an engine while the vehicle is at rest and
then launch the vehicle solely under the power of first prime mover 22 or under parallel power
(i.e., combined power of first and second prime movers 22, 26). Optionally, when second prime
mover 26 is directly connected to first power path 54 via planetary gearset 48, first prime mover
22 may be shut down and the vehicle operated solely under the power of second prime mover
26, provided second prime mover 26 is appropriately configured for this mode of operation.
[0029] Referring to FIGS. 5 and 6, another embodiment of hybrid powertrain system 20 is
shown that includes a hybrid transmission 24'. In the illustrated embodiment, main clutch 28
includes first clutch portion 202 having a main clutch input shaft 204 and a main clutch output
shaft 206, which also functions as the input shaft to multi-ratio transmission 52 (not shown in
FIGS. 5 and 6). A portion of main clutch output shaft 206 is rotatably supported within a
portion of main clutch input shaft 204 by an overrunning clutch 208. Main clutch 28 also
includes a second clutch portion 210 having a housing member 212 that surrounds at least a

portion of first clutch portion 202 and an output shaft 214 that surrounds main clutch output
shaft 206 and is concentric with respect thereto. Second clutch portion 210 includes a clutch
216, such as a hydraulically or electrically operated friction clutch.
[0030] Second prime mover 26 is shown in FIG. 5 as an electric motor/generator having a
rotor 218 secured for rotation with output shaft 214 and a stator 220. However, other sources of
motive power may be used in place of an electric motor/generator, such as a hydraulic
motor/pump. In hybrid transmission 24', second prime mover 26 is selectively connectable to
main clutch output shaft 206 through a planetary gearset 222. When so configured, output shaft
»
214 includes a sun gear 224 secured for rotation therewith and main clutch output shaft 206
includes an axially moveable ring gear 226, a portion of which is splined for rotation with main
clutch output shaft 206. Between sun gear 224 and ring gear 226 are a number of planet gears
228 meshed with sun gear 224 and ring gear 226. Planet gears 228 are rotatably supported by a
planet carrier 230, which in turn is rotatably supported by an overrunning clutch 232 that is
secured to the transmission housing or other fixed structure. Second prime mover 26 is also
selectively connectable to main clutch output shaft 206 through ring gear 226, which includes a
tongue and groove type arrangement 233 or other interlocking arrangement that locks output
shaft 214 for rotation with main clutch output shaft 206 when ring gear 226 is moved from the
"unlocked" position shown in FIG. 5 to the "locked" position shown in FIG. 6. Ring gear 226
may be moved by an actuator mechanism (not shown), such as a mechanism similar to the one
shown in FIGS. 2-4.
[0031] As shown in FIG. 5, planetary gearset 222 is arranged so that when second prime
mover 26 is operating to rotate output shaft 214 in a first direction (such as the counterclockwise
direction illustrated in FIG. 5) and clutches 208 and 216 are "disengaged", planet carrier 230 is
prohibited from rotating by "engaging" clutch 232, causing the rotational power from output
shaft 214 to be transmitted through planet gears 228 and into ring gear 226 at a predetermined
gear ratio. Rotational power is transmitted into main clutch output shaft 206 through ring gear
226 and then into multi-ratio transmission 52. In this mode of operation, second prime mover 26
may be operated to launch a vehicle employing hybrid transmission 24' without the assistance of
first prime mover 22.

[0032] When the desired vehicle speed is achieved, the rotation of output shaft 214 is
reversed (see, e.g., FIG. 6), allowing overrunning clutch 232 to he "disengaged", planetary
gearset 222 to freewheel and clutch 208 to be "engaged". Rotational power may then be
transferred from second prime mover 26 through output shaft 214 and into main clutch input
shaft 204 via clutch 208. In this mode of operation, rotational power from second prime mover
26 may be used to start first prime mover 22 functioning as an internal combustion engine.
[0033] When second prime mover 26 functions as an electric motor/generator or a hydraulic
motor/generator, rotation of output shaft 214 may be quickly reversed to facilitate tire transfer of
power from main clutch output shaft 206 to main clutch input shaft 204. Thus, when the motor
speed decreases to zero (during the transition from one rotating direction to another) and then
begins to increase in the other direction, clutch 216 picks the engine up and begins cranking it
and driving it toward the speed of the transmission input shaft (main clutch output shaft 206),
which is being maintained by vehicle inertia. When first prime mover 22 starts, the speed of
first prime mover 22 is quickly increased under the assistance of second prime mover 26, which
provides for a relatively smooth start and engine acceleration sequence. Clutch 208 engages
when the speed of main clutch input shaft 204 and main clutch output shaft 206 are substantially
equal. During the time main clutch input shaft 204 is accelerating, there is generally no power
being applied to main clutch output shaft 206, allowing a gear ratio change to occur in multi-
ratio transmission 52. In a vehicle employing an internal combustion engine as the first prime
mover and an electric/hydraulic motor as the second prime mover 26, the above event results in
a smooth and efficient switch from all electric/hydraulic drive, to engine-electric/hydraulic
' parallel drive, all while starting the engine and conducting a gear ratio change in the
transmission virtually simultaneously.
[0034] Clutch 208 is a one-way clutch, which allows "positive" driveline torque to flow
through clutch 208 in a direction from first prime mover 22 toward hybrid transmission 52 and
prevents torque-flow in the opposite direction. Clutch 216 can remain engaged if desired to
provide torque flow in the opposite direction. However, when clutch 216 is disengaged, clutch
208 acts in its capacity as a one way clutch. The nature of clutch 208 allows first prime mover .
22 to be reduced to an idle speed or shut down any time it is not providing positive driveline
torque. As noted above, in conventional non-hybrid drivetrains, negative driveline torque is

absorbed by the vehicle engine and/or brakes and is therefore lost energy. However, in hybrid
transmission 24', this torque may be absorbed by the second prime mover 26 and used to drive
rotation of second prime mover 26 operating as a generator or pump to create and store energy in
energy storage device 38B. At the same time, prime mover 26 may also emulate engine braking
and the engine braking feature may be desired, if storage device 38B has reached capacity.
Clutch 216 may remain engaged and normal engine braking will occur. Otherwise, clutches
208, 216 and 232 may be disengaged and ring gear 226 moved (as shown in FIG. 6) to directly
connect output shaft 214 for rotation with main clutch output shaft 206 through tongue and
groove arrangement 233. In this mode of operation, negative driveline torque may be
transmitted from main clutch output shaft 206 into second prime mover 26 via output shaft 214.
Optionally, when second prime mover 26 is directly connected to main clutch output shaft 206
via output shaft 214, first prime mover 22 may be shut down and the vehicle operated solely
under the power of second prime mover 26, provided the motor is appropriately configured for
this mode of operation.
[0035] Among other features, hybrid transmission 24,24' may be readily installed in an
existing vehicle driveline. Once installed, the present invention provides for rolling engine start
features in hybrid vehicles and allows the vehicle to be operated solely under the power of
second prime mover 26, while maintaining the normal operating characteristics of the vehicle
driveline, such as normal vehicle clutching and/or automated transmission operation. Further,
when the first prime mover torque, planet gearset ratio, and second prime mover torque are
properly matched, a desirable and tailored feel can be achieved at the time when first prime
mover, second prime mover and the driveline come together in parallel operation. This feature
is accomplished, for example, by configuring hybrid powertrain system such that the sum of the
first and second prime mover torque is substantially similar to second prime mover torque times
the planetary gearset ratio.
[0036] The hybrid powertrain system of the present invention also provides for the shortest
possible torque interruption during an engine start-up sequence. This feature is supported by the
electric/hydraulic motor's ability to reverse direction quickly to change modes of operation,
which includes a gear ratio change, rather than using more traditional clutches that have to be
trimmed and controlled. Thus, first prime mover 22 operating as a heavy duty diesel engine may

be stalled and brought up to operating speed without the roughness experienced in non-motor
assisted diesel engine start and acceleration sequences.
[0037] The present invention has been particularly shown and described with reference to
the foregoing embodiments, which are merely illustrative of the best modes for carrying out the
invention. It should be understood by those skilled in the art that various alternatives to the
embodiments of the invention described herein may be employed in practicing the invention
without departing from the spirit and scope of the invention as defined in the following claims.
It is intended that the following claims define the scope of the invention and that the method and
apparatus within the scope of these claims and their equivalents be covered thereby. This
description of the invention should be understood to include all novel and non-obvious
combinations of elements described herein, and claims may be presented in this or a later
application to any novel and non-obvious combination of these elements. Moreover, the
foregoing embodiments are illustrative, and no single feature or element is essential to all
possible combinations that may be claimed in this or a later application.

WE CLAIM
1. A vehicular hybrid powertrain system (20), comprising:
a first prime mover (22) having an output;
a multi-ratio transmission (52) having an input (44);
a second prime mover (26) having an output operably connected to
the transmission (52) input (44) through a first power path (54) and to
the first prime mover (22) output through a second power path (56), the
first power path (54) configured to receive power from the second prime
mover (26) during a first operating mode to drive rotation of the
transmission (52) input (44) and the second power path (56) configured
to receive power from the second prime mover (26) during a second
operating mode to drive rotation of the first prime mover (22) output; and
wherein the second prime mover (26) output is configured to rotate in
a first direction in the first operating mode to transmit power to the first
power path (54) and in a second direction opposite the first direction in
the second operating mode to transmit power to the second power path
(56).
2. The hybrid powertrain system (20) as claimed in claim 1, wherein the first
mode of operation includes launching the vehicle in a first transmission
ratio solely under the power produced by the second prime mover (26).
3. The hybrid powertrain system (20) as claimed in claim 1, wherein the
second mode of operation includes starting the first prime mover (22)
when the first prime mover (22) is an internal combustion engine,

changing the transmission ratio from a first transmission ratio to a
second transmission ratio and operating the first (22) and second (26)
prime movers in parallel.
4. The hybrid powertrain system (20) as claimed in claim 1, wherein a
second prime mover (26) driven countershaft (70) for transmitting power
from the second prime mover (26) to the first (54) and second (56) power
paths.
5. The hybrid powertrain system (20) as claimed in claim 4, wherein a first
overrunning clutch (78) positioned between the countershaft (70) and the
second power path (56), the first overrunning clutch (78) configured to
engage and transmit power from the second prime mover (26) to the
second power, path (56) when the countershaft (70) is rotating in a first
direction and to disengage and prohibit power from being transmitted
from the second prime mover (26) to the second power path (56) when
the countershaft (70) is rotating in a second direction opposite the first.
6. The hybrid powertrain system (20) as claimed in claim 5, wherein a collar
(74) rotatably supported on the countershaft (70) between the first
overrunning clutch (78) and the countershaft (70).
7. The hybrid powertrain system (20) as claimed in claim 6, wherein a first
axially movable clutch (72) adapted to selectively secure the collar (74)
for rotation with the countershaft (70).

8. The hybrid powertrain system (20) as claimed in claim 4, wherein a
second overrunning clutch (90) positioned between the first prime mover
(22) output and the transmission (52) input (44), the second overrunning
clutch (90) configured to engage and transmit power between the first
prime mover (22) output and the transmission (52) input (44) when the
first prime mover (22) output and the transmission (52) input (44) are
rotating at a first predetermined speed and to disengage and prohibit
power from being transmitted between the first prime mover (22) output
and the transmission (52) input (44) when the first prime mover (22)
output and the transmission (52) input (44) are rotating at a second
predetermined speed.
9. The hybrid powertrain system (20) as claimed in claim 8, wherein the
second overrunning clutch (90) is configured to engage when the
transmission (52) input (44) speed is substantially equal to the first prime
mover (22) output speed.
10.The hybrid powertrain system (20) as claimed in claim 4, wherein a
planetary gearset (48) selectively interconnecting the countershaft (70)
and the first power path (54).
11.The hybrid powertrain system (20) as claimed in claim 10, wherein the
planetary gearset (48) includes a third overrunning clutch (116)
configured to engage when the countershaft (70) is rotating in the first
direction to transmit power through the planetary gearset (48) and into
the first power path (54) and to disengage when the countershaft (70) is
rotating in the second direction.

12.The hybrid powertrain system (20) as claimed in claim 4, wherein a
second axially moveable clutch (91) for selectively interconnecting the
countershaft (70) and the first power path (54).
13.The hybrid powertrain system (20) as claimed in claim 1, wherein the first
(54) and second (56) power paths are gear trains.
14.The hybrid powertrain system (20) as claimed in claim 1, wherein:
a second prime mover (26) driven countershaft (70) for transmitting
power from the second prime mover (26) to the first (54) and second (56)
power paths;
a first overrunning clutch (78) positioned between the countershaft
(70) and the second power path (56), the first overrunning clutch (78)
configured to engage and transmit power from the second prime mover
(26) to the second power path (56) when the countershaft (70) is rotating
in a first direction and to disengage and prohibit power from being
transmitted from the second prime mover (26) to the second power path
(56) when the countershaft (70) is rotating in a second direction opposite
the first;
a second overrunning clutch (90) positioned between the first prime
mover (22) output and the transmission (52) input (44), the second
overrunning clutch (90) configured to engage and transmit power
between the first prime mover (22) output and the transmission (52) input
(44) when the first prime mover (22) output and the transmission (52)
input (44) are rotating at a first predetermined speed and to disengage
and prohibit power from being transmitted between the first prime mover

(22) output and the transmission (52) input (44) when the first prime
mover (22) output and the transmission (52) input (44) are rotating at a
second predetermined speed;
15. A method of operating a vehicular hybrid powertrain system (20),
comprising:
providing a first prime mover (22) having an output, a multi-ratio
transmission (52) having an input (44), and a second prime mover (26)
having an output operablv connected to the transmission (52) input (44)
through a first power path (54) and to the first prime mover (22) output
through a second power path (56), the first power path (54) configured to
receive power from the second prime mover (26) during a first operating
mode to drive rotation of the transmission (52) input (44) and the second
power path (56) configured to receive power from the second prime
mover (26) during a second operating mode to drive rotation of the first
prime mover (22) output;
rotating the output of the second prime mover (26) in a first direction
during the first mode of operation to drive rotation of the transmission
(52) input (44); and
rotating the output of the second prime mover (26) in a second
direction opposite the first direction during the second mode of operation
to drive rotation of the first prime mover (22) output.
16.The method as claimed in claim 15, wherein the first mode of operation
includes launching the vehicle in a first transmission ratio.

17. The method as claimed in claim 15, wherein the second mode of
operation includes starting the first prime mover (22) when the first prime
mover (22) is an internal combustion engine, changing the transmission
ratio from a first transmission ratio to a second transmission ratio and
operating the first (22) and second (26) prime movers in parallel.
18.The method of as claimed in claim 15, wherein:
providing a second prime mover (26) driven countershaft (70) for
transmitting power from the second prime mover (26) to the first (54) and
second (56) power paths, a first overrunning clutch (78) positioned
between the countershaft (70) and the second power path (56), the first
overrunning clutch (78) configured to engage and transmit power from
the second prime mover (26) to the second power path (56) when the
countershaft (70) is rotating in a first direction and to disengage and
prohibit power from being transmitted from the second prime mover (26)
to the second power path (56) when the countershaft (70) is rotating in a
second direction opposite the first, and a second overrunning clutch (90)
positioned between the first prime mover (22) output and the
transmission (52) input (44), the second overrunning clutch (90)
configured to engage and transmit power between the first prime mover
(22) output and the transmission (52) input (44) when the first prime
mover (22) output and the transmission (52 ) input (44) are rotating at a
first predetermined speed and to disengage and prohibit power from
being transmitted between the first prime mover (22) output and the
transmission (52) input (44) when the first prime mover (22) output and
the transmission (52) input (44) are rotating at a second predetermined
speed; and

engaging the first overrunning clutch (78) and rotating the output of
the second prime mover (26) in the second direction opposite the first
direction during the second mode of operation to drive rotation of the first
prime mover (22) output.
19. The method as claimed in claim 18, wherein engaging the second
overrunning clutch (90) when the speed of the first prime mover (22)
output and the transmission (52) input (44) are substantially equal.
20. The method as claimed in claim 18, the second prime mover (26)
selectively absorbing negative driveline torque, the negative driveline
torque providing at least one of power generation and emulated engine
braking.

ABSTRACT

A VEHICLE HYBRID POWER TRAIN SYSTEM AND METHOD OF
OPERATING THE SAME
A hybrid powertrain system (20) includes a first prime mover (22) having an
output, a multi-ratio transmission (52) having an input (44), and a second prime
mover (26) having an output connected to the first prime mover (22) output
through a first power path (54) and to the transmission (52) input (44) through a
second power path (56). The first power path (54) receives power from the
second prime mover (26) during a first operating mode to drive rotation of the
transmission (52) input (44) and the second power path (56) receives power
from the second prime mover (26) during a second operating mode to drive
rotation of the first prime mover (22) output. The second prime mover (26)
output is configures to rotate in a first direct JIon in the first operating mode to
transmit power to the first power path (54) and in a second direction in the
second operating mode to transmit power to the second power path (56).